1. Field of the Invention
The present invention relates to a data recording and reproducing apparatus and method for recording and reproducing video data and the like.
2. Description of the Related Art
In recent years, in association with the increase in the number of channels of providing information because of the widespread of CATVs (community antenna television or cable televisions) and the like, different from a VCR (Video Cassette Recorder) of a related art, the demand of simultaneously reproducing plural video and audio data from a single video and audio data recording and reproducing apparatus is increasing. In order to satisfy the demand, an apparatus called an audio video (hereinbelow, also referred to as xe2x80x9cAVxe2x80x9d) server for recording and reproducing video and audio data by using recording and reproducing media which are randomly accessible such as hard disks is being spread.
Generally, for example, in an AV server in a broadcasting station, a data transfer rate required is high due to a demand of the image quality and sound quality and the capacity has to be large to record data of long hours. Therefore, an attempt to realize higher data transfer rate and larger capacity by using a data recording and reproducing apparatus including a plurality of hard disk drives (hereinbelow, referred to as HDDs) which store video and audio data and can be operated in parallel and an attempt to assure the reliability by recording parity data even if any of the HDDs gets out of order are made. Consequently, even when the number of channels required differs according to the contents of programs which broadcasting stations are providing and broadcasting modes, a multi-channel AV server which can accommodate various usage patterns such as a pattern of recording plural material data in a distributed manner and simultaneously transmitting the data to multichannels and a pattern of constructing a near video on demand (NVOD) system by reproducing the same material data by deviating reproduction time through multichannels can be realized.
In the data recording and reproducing apparatus which is used for such a multichannel AV server, the RAID (Redundant Arrays of Inexpensive Disks) technique proposed in xe2x80x9cA Case for Redundant Arrays of Inexpensive Disks (RAID)xe2x80x9d, ACM SIGMOD Conference, Chicago, Ill., Jun. 1 to 3, 1988 by Patterson, D. A., Gibson, G., and Kats, R. H is employed. In the paper, RAID is classified into five classes of RAID-1 to RAID-5. Among them, representative ones are RAID-1, RAID-3, and RAID-5. As a classification for explanation, there is RAID-0 as well. RAID-0 relates to a method of operating a plurality of hard disks in parallel.
RAID-1 relates to a method of writing the same contents into two hard disks. RAID-3 relates to a method of dividing input data in predetermined length, recording divided data into a plurality of HDDs, generating parity data, and writing the parity data into another HDD. Meanwhile, RAID-5 relates to a method of setting a larger data dividing unit (block), recording one divided data as a data block into one HDD, recording the result (parity data) of the exclusive OR of data blocks corresponding each other in the HDDs as a parity block to another HDD, and distributing the parity block to all of the HDDs.
FIG. 1 is a construction diagram showing an example of the construction of an AV server using the RAID technique. An AV server 100 is used as a CM (commercials) transmitting apparatus, a news editing apparatus, or the like for providing multiple inputs and outputs of plural image data. The AV server 100 comprises a plurality of disk array apparatuses 1101 to 1104 for recording input image data and a processor 120 for inputting image data to be recorded on each of the disk array apparatuses 1101 to 1104 and outputting the image data reproduced from each of the disk array apparatuses 1101 to 1104.
In the AV server 100, for example, each of plural input image data DIl to DIn (n is an integer value of 2 or larger) inputted from a video device 121 or a transmitter-receiver 122 for satellite channels is recorded into at least one of the disk array apparatuses 1101 to 1104. As required, the data recorded in the disk array apparatuses 1101 to 1104 is reproduced and outputted as output data D01 to D0n to, for example, a video monitor 123 or a transmitter-receiver 124 for satellite channels.
FIG. 2 is an explanatory diagram showing an example of the structure of a disk array apparatus 110 (shown as a representative of 1101 to 1104). The disk array apparatus 110 comprises a plurality of HDDs 1311 to 1315 and a disk array controller 130 for controlling the HDDs 1311 to 1315. In the disk array apparatus 110, data in a predetermined unit (for example, a frame or GOP (Group Of Picture) unit) is written/read in parallel to/from the HDDs 1311 to 1315. The structure in which data is simply read and written in parallel is according to the method of RAID-0. In case of the method of RAID-3, one of the plurality of the HDDs 1311 to 1315 is dedicated to parity data. Although five HDDs 1311 to 1315 are shown in FIG. 2, the number of HDDs is not limited to five.
In the disk array apparatus 110, the inputted image data DI of, for example, one frame is divided, for instance, on a byte unit basis by the disk array controller 130 and the divided data is sequentially written in parallel onto hard disks in the HDDs 1311 to 1315 by the HDDs 1311 to 1315. FIG. 2 illustrates a case where data F1 in the first frame and data F2 of the second frame are written in parallel onto the hard disks in the HDDs 1311 to 1315. In the disk array apparatus 110, when data recorded in the HDDs 1311 to 1315 is reproduced, the data is reproduced from the HDDs 1311 to 1315 by the disk array controller 130. The reproduced data is arranged in the same order as the order upon input, formed as a collection of data, and outputted as reproduction data D0.
In the disk array apparatus 110, in order to reduce the influence of seek (seeking operation) time of data in the HDDs 1311 to 1315, a certain amount (for example, few tens of frames) of data has to be accessed (read/written) in a lump per time.
Meanwhile, in the data recording and reproducing apparatus represented by the AV server 100, there is a case that variable speed reproduction of recorded data is desired to be performed. In this case, the data recording and reproduced apparatus of the related art has problems such that information necessary for the variable speed reproduction at a desired speed cannot be obtained and an information dropout occurs in a reproduction image due to the variable speed reproduction for the following reasons.
For example, in the data recording and reproducing apparatuses according to the RAID-0 and RAID-3 methods, data is written/read in parallel to/from HDDs on a unit image basis. In case of performing the variable speed reproduction, it takes time to seek image data to be reproduced next (for example, about 10 to 20 msec) every unit image. As the data reading speed, for example, the performance of about 3 frames/100 msec is the limit. In the AV server 100 which is basically multi-accessible, therefore, data can be outputted only with the performance of about few frames/second. There is consequently a problem such that information of 30 frames/second which is normally necessary cannot be acquired.
For example, in a data recording and reproducing apparatus employing RAID-5, since each unit image is recorded in individual HDD, different from the RAID-0 and RAID-3 methods, a problem caused by the seek operation does not occur. For example, however, in case of reproducing continuous frame data of frames F1, F2, F3, . . . at double speed, skipped data of frames F1, F3, F5, F7, F9, . . . is outputted, so that there is a problem such that information of data of frames F2, F4, F6, F8, . . . is not outputted. For example, in case of reproducing data at quadruple speed, data of frames F1, F5, F9, . . . is outputted and information is further dropped out. Consequently, as the reproduction speed increases, the dropout in information becomes larger. Such an information dropout similarly occurs in the RAID-0 and RAID-3 methods.
In case of performing the variable speed reproduction in a VCR, there is a part called a guard band which is not magnetized between recording tracks on a video tape. Although there is a gap in a recording area, information regarding all of frames is included in a divided state in the reproduction image. Consequently, for example, there is an advantage such that information recorded instantaneously in the image like an image of a flashed part can be retrieved while performing a variable speed reproduction. On the other hand, in the data recording and reproducing apparatus, since a dropout in the information occurs on a frame unit basis, in case of retrieving a specific scene during the variable speed reproduction, there is a case that the target scene cannot be retrieved for the reason as described above.
The present invention is achieved in consideration of the problems and its object is to provide a data recording and reproducing apparatus and method capable of easily obtaining information which has few dropout and is necessary for variable speed reproduction at the time of variable speed reproduction.
A data recording and reproducing apparatus according to the invention comprises: data dividing means for dividing input image data into a plurality of parts on a predetermined data unit basis, thereby generating data divided in a plurality of groups; recording and reproducing means for recording the divided data onto a plurality of recording media divided in a plurality of groups in correspondence with the number of groups of the divided data and reproducing the recorded divided data as required; image data forming means for forming desired image data on the basis of the divided data reproduced by the recording and reproducing means; and control means for controlling the recording and reproducing means so that the divided data of each group is recorded onto the recording media of the different groups respectively, while the relation between the groups of the divided data and the groups of the recording media is periodically changed in a predetermined pattern on the predetermined data unit basis.
A data recording and reproducing method according to the invention comprises the steps of: dividing input image data into a plurality of parts on a predetermined data unit basis, thereby generating data divided in a plurality of groups; recording the divided data onto a plurality of recording media on a group unit basis so as to be recorded onto the recording media of a different group respectively, while periodically changing the relation between the groups of the divided data and the groups of a plurality of recording media grouped in correspondence with the number of groups of the divided data, and reproducing the recorded divided data as required; and forming desired image data on the basis of the divided data reproduced.
In the recording and reproducing apparatus of the invention, input image data is divided into a plurality of parts on a predetermined data unit basis by the data dividing means. The recording and reproducing means is controlled by the control means to record the divided data in groups onto the recording media of different groups while periodically changing the relation between the groups of the divided data and the groups of the plurality of recording media grouped in correspondence with the number of groups of the divided data in a predetermined pattern on the predetermined data unit basis.
In the data recording and reproducing method according to the invention, input image data is divided into a plurality of parts on a predetermined data unit basis, thereby forming divided data divided in a plurality of groups. Recording is performed to the plurality of recording media so that the divided data is recorded on a group unit basis into the recording media of different groups while the relation between the groups of the divided data and the groups of the plurality of recording media divided into a plurality of groups in correspondence with the number of groups of the divided data is periodically changed in a predetermined pattern on a predetermined data unit basis, the recorded divided data is reproduced as required, and desired image data is formed on the basis of the reproduced divided data.
Other and further objects, features and advantages of the invention will appear more fully from the following description.